[ADMIN] Character codification

[Sistemas C.M.P.]

I'm using Linux server with postgres 8.0.2 and windows clients with VB 
aplications that using pgOleDB.dll and Libpq.dll.
The problem is: 
 Some user updates a record (with Text type field) with '?' character in this 
field
Then, when someone select this record the '?' characters appears like '$1'
This only happen with a few users. Not all
                    Thanks.